Classifications

• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
  • C12P7/00—Preparation of oxygen-containing organic compounds
  • C12P7/02—Preparation of oxygen-containing organic compounds containing a hydroxy group
  • C12P7/04—Preparation of oxygen-containing organic compounds containing a hydroxy group acyclic
  • C12P7/06—Ethanol, i.e. non-beverage
  • C12P7/08—Ethanol, i.e. non-beverage produced as by-product or from waste or cellulosic material substrate
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
  • C12P7/00—Preparation of oxygen-containing organic compounds
  • C12P7/02—Preparation of oxygen-containing organic compounds containing a hydroxy group
  • C12P7/04—Preparation of oxygen-containing organic compounds containing a hydroxy group acyclic
  • C12P7/06—Ethanol, i.e. non-beverage
  • C12P7/065—Ethanol, i.e. non-beverage with microorganisms other than yeasts
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
  • C12P7/00—Preparation of oxygen-containing organic compounds
  • C12P7/02—Preparation of oxygen-containing organic compounds containing a hydroxy group
  • C12P7/04—Preparation of oxygen-containing organic compounds containing a hydroxy group acyclic
  • C12P7/06—Ethanol, i.e. non-beverage
  • C12P7/14—Multiple stages of fermentation; Multiple types of microorganisms or re-use of microorganisms
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E50/00—Technologies for the production of fuel of non-fossil origin
  • Y02E50/10—Biofuels, e.g. bio-diesel

Definitions

• the present invention relates to a process for the production of ethanol comprising both gasification and fermentation of suitable feedstocks.
• US 5,753,474 describes a continuous two-stage anaerobic fermentation process to produce butanol using two different strains of bacteria.
• a number of bacteria which can produce ethanol from the carbon oxides and hydrogen in such a process, and the selectivity to ethanol may be controlled both by selection of bacteria and by control of the reaction conditions, generally to keep the bacteria functioning and to favour ethanol production over competing products, such as acetic acid.
• Specific examples of bacteria and processes can be found in US 2003/0211585 and US 2007/0275447 .
• ethanol may be advantageously produced from biomass feedstocks via a process in which both a gasification step and a first fermentation step are applied to the initial biomass, with at least one further fermentation step applied to the products from the gasification and first fermentation step to produce ethanol.
• the present invention provides a process for the production of ethanol, said process comprising:
• the present invention provides a number of advantages over the known processes for the production of ethanol from biomass via gasification, especially as described in US 2003/0211585 and US 2007/0275447 .
• processes for production of ethanol from biomass via gasification tend to be net CO 2 producers.
• This CO 2 production may actually arise from either step of the process.
• the gasification step itself generally produces CO 2 as well as CO and H 2 .
• fermentation routes to higher alcohols (ethanol and heavier alcohols) from carbon monoxide may, in theory, utilise CO 2 as a reactant for the production of the higher alcohols, in practise the fermentation reaction also tends to be a net producer of carbon dioxide.
• the bacteria used for fermentation can produce alcohols according to either of the following 2 reactions: (1) 6CO + 3H 2 O ⁇ C 2 H 5 OH + 4CO 2 (2) 2CO 2 + 6H 2 ⁇ C 2 H 5 OH + 3H 2 O
• the CO conversion is typically 70-90% per pass while the H 2 conversion is typically less than the CO conversion - therefore fermentation is also a net producer of CO 2 , the overall gasification and syngas fermentation process tending to produce several moles of CO 2 for every mole of ethanol produced.
• the gasification step in the process of the present invention is still important however since many feedstocks (or components of potential feedstocks) cannot be fermented, but are gasifiable.
• feedstocks are non-biomass feedstocks, such as plastics, and non-fermmtable biomass feedstocks, such as lignins.
• the biomass feedstock passed to the first fermentation step and the gasifiable feedstock passed to a gasification step derive from a single mixed waste feed comprising both fermentable and gasifiable components.
• a mixed waste feed comprising both fermentable and gasifiable (but non-fermentable) components, whilst minimising environmental impact compared to use of gasification of such feedstocks alone.
• a mixed waste feed after separation to remove recyclable materials such as glass, may be treated to separate a first feedstock comprising fermentable components for use as the biomass feedstock for the first fermentation step of the present invention, and a second feedstock comprising gasifiable components for use as the gasifiable feedstock for the gasification step of the present invention.
• the gasifiable feedstock for the gasification step of the present invention may comprise residual components, for example non-fermentable components, from the first fermentation step i.e. a biomass feedstock may be subjected to the first fermentation step to produce a solution comprising acetic acid and a solid residual which solids are passed as the gasifiable feedstock for the gasification step of the present invention.
• the present invention utilises a first fermentation step to produce a product comprising acetic acid, reducing the carbon dioxide footprint of a process using just a gasifier with fermentation of the carbon monoxide and hydrogen produced on the initial feedstock.
• the biomass feedstock in step (a) may be any suitable biomass feedstock including, but not limited to, municipal solid waste, lignocellulosic biomass, landfill leachate, carbohydrates, fats and proteins. Specific examples are the biodegradable portion of municipal and industrial wastes, bio-sludge, energy crops and agricultural residues.
• the feedstock may be treated by conventional means, such as milling, to make it more easily digested during fermentation.
• the feedstock is not pasteurised or sterilised to remove bacteria therefrom, such a process not being necessary in the present invention.
• sterilize means to treat to effectively kill all bacteria therein. This is typically achieved by application of heat, although other means, such as irradiation, are also known.
• pasteurisation means to treat for the purpose of killing bacteria to achieve a 5-log reduction (0.00001 times the original) in the number of live bacteria.
• Pasteurisation can be distinguished from sterilisation in that some bacteria survive the process.
• Pasteurisation is typically also performed by the application of heat, generally at lower temperature and/or for a shorter period of time than a corresponding sterilisation.
• other means such as irradiation, are also known.
• the feedstock pre-treatment is generally selected dependent on the specific feedstock and as necessary or advantageous to make the feedstock more suitable for fermentation. Typically this involves methods to effect size reduction in order to provide improved access for the bacteria and improve the rate of conversion. Examples of known techniques are shredding, milling, ultrasound, hydrocrushing, steam explosion.
• the treatment may also include treatment to remove or reduce gasifiable but non-fermentable components which can then be passed to the gasification step of the present invention.
• the biomass feedstock is subjected to anaerobic fermentation under conditions to convert (ferment) biomass to a solution comprising acetic acid.
• a single bacterial strain may be used, but generally the most effective processes use a mixture of bacterial strains.
• a particular advantage of the use of a mixture of bacterial strains is that the first fermentation step can be applied widely to different types ofbiomass because of the mixture of bacterial strains present.
• the mixture of bacterial strains may include bacterial strains present in the biomass feedstock. As noted above, therefore, the feedstock need not be pasteurised or sterilised to remove bacteria therefrom.
• hydrolysis There are four key stages in normal anaerobic digestion: hydrolysis, acidogenesis, acetogenesis and methanogenesis.
• hydrolysis complex organic molecules are broken down into simple sugars, acids and amino acids. Bacteria convert these molecules to volatile fatty acids through the process of acidogenesis.
• acetogenesis of the volatile fatty acids occurs and they are converted to carboxylic acids, such as acetic acid and butyric acid.
• carboxylic acids such as acetic acid and butyric acid.
• methanogenesis is methanogenesis, in which acetic acid is broken down to form methane and carbon dioxide.
• the bacteria present in anaerobic digestion can be classified by the final product as either acetogens or methanogens. Both types are likely to be present in step (a) of the present invention.
• the conditions in the first fermentation step are maintained to favour a product comprising acetic acid, which effectively means conditions that inhibit any methanogenic bacteria.
• the principal condition necessary for this is the pH, and in the process of the present invention the pH is maintained below 6.0, preferably at a pH in the range 3 to 5.5. At this pH the methanogenic bacteria are inhibited in their activity and reproduction.
• acetogenic bacteria also prefer higher temperatures than methanogenic bacteria. Therefore, whilst temperatures in the range 20 to 70°C may be utilised, preferably the temperature in the first fermentation step is in the range 40 to 60°C, which further inhibits the methanogenic bacteria.
• the acetic acid is the predominant product from step (a), by which is meant that acetic acid is present in higher concentration than any other products.
• the acetic acid is present in a concentration of at least 60 wt%, preferably at least 80 wt% of the total weight of carboxylic acids in the product stream.
• the second most predominant product is usually butyric acid.
• the product stream comprises at least a 2:1 ratio of acetic acid to butyric acid.
• the product stream may comprise at least a 4:1 ratio of acetic acid to butyric acid and a concentration of the acetic acid of at least 90 wt% of the total weight of carboxylic acids in the product stream.
• Nutrients may be added to the first fermentation step as and if required. For example, whilst most manures and complex feedstocks usually inherently contain sufficient nutrients for the bacteria in step (a), other feedstocks, such as industrial wastes and crop residues may be deficient. Typical nutrients requirements include nitrogen, phosphorous, magnesium, sodium, manganese, calcium and cobalt. Nutrients are preferably added by mixture of nutrient rich feedstocks, such as manure, with those that may be nutrient-deficient.
• step (a) is bulk fermentation of a biomass pile as described in US 2006/0024801 , but any suitable fermentation tank or vessel may also be used.
• a number of fermentation tanks/vessels are commercially available, such as the Induced Blanket Reactor available from Andigen LC of Ohio, USA.
• Step (a) produces an initial product solution comprising acetic acid, bacteria and residual solids which can be removed from the first fermentation step. Typically, this product solution is separated from any residual solids to produce a solution comprising the acetic acid suitable for use in step (c).
• a suitable means of separation for any residual solids is filtration.
• the separated residual solids may be passed as all or part of the gasifiable feedstock in step (b).
• bacteria from the first fermentation step are also separated.
• bacteria may be separated by filtration with a suitably small mesh filter.
• the solution may be pasteurised or sterilised.
• the product stream from step (a) is removed in the form of a dilute solution in water.
• the solution preferably has a concentration of acetic acid in solution of 1 to 5 wt%, more typically 2 to 5 wt%.
• concentration of products in said stream can be controlled by the rate at which the product stream is removed from the fermentation.
• the acetic acid may inhibit formation of further acid, even to the extent that the acids can kill the bacteria.
• the solution removed from step (a) is relatively dilute, no concentration is required before the subsequent fermentation to produce ethanol therefrom.
• step (b) of the process of the present invention a gasifiable feedstock is passed to a gasification step and subjected to a gasification to produce a gaseous mixture comprising carbon monoxide and hydrogen.
• the gasifiable feedstock may be any suitable gasifiable feedstock.
• the preferred gasifiable feedstock comprises waste plastics and/or non-fermentable components of a mixed waste feed, the fermentable components of which are passed to the first fermentation step as the biomass feedstock in step (a).
• co-feeds such as methane or coal.
• Methane for example, can be fed to the gasification step to increase the H 2 :CO ratio obtained from the gasification.
• the first fermentation step is operated to favour acid formation and inhibit methane formation, if any methane is formed in the first fermentation step this may be cycled to the gasification step.
• the process of the present invention is applied to a mixed waste feed obtained from or at a landfill site.
• a landfill site produces what is termed "landfill gas" which is a mixture of predominantly methane, carbon dioxide and hydrogen sulphide, and which must normally be reformed or combusted in an on-site facility.
• this landfill gas may be passed as a co-feed to the gasification step (b) along with the non-fermentable components of the landfill derived mixed waste feed (gasifiable feedstock).
• the landfill gas may be passed to the gasification step without treatment.
• Any suitable gasification process may be used in the gasification step.
• a large number of gasification processes are known to the person skilled in the art.
• representative examples of suitable processes include those described in WO 2007/143673 , WO 2007/131241 and US 6,817,388 .
• step (c) of the process of the present invention the solution comprising acetic acid from step (a) and the gaseous mixture from step (b) are passed to one or more further fermentation steps wherein they are subject to fermentation to produce ethanol.
• the solution comprising acetic acid from step (a) and the gaseous mixture from step (b) are passed to separate fermentation steps.
• the solution comprising acetic acid from step (a) may be passed to a fermentation step wherein it is contacted with a bacteria capable of converting acetic acid to ethanol, whilst the gaseous mixture from step (b) is passed to a fermentation step for the production of ethanol from carbon monoxide and hydrogen utilising an anaerobic acetogenic bacteria.
• solventogenesis The conversion of carboxylic acids to their corresponding alcohols, known as solventogenesis is described, for example, in US 5,853,474 .
• a number of bacteria, hereinafter defined as solventogenic bacteria, which are capable of converting carboxylic acids to their corresponding alcohols are known and any such solventogenic bacteria may be used. Particularly suitable examples are Clostridium acetobutylicum, C. beijerinkii, C. aurantibutyricum, and C tetanomorphum. Clostridium acetobutylicum is most preferred.
• the anaerobic acetogenic bacteria for this step are not especially limited as long as they are able to convert CO and H2 into ethanol.
• Useful bacteria include, without limitation, those described in US 2003/0211585 and US 2007/0275447 , namely Acetogenium kivui, Acetobacterium woodii, Acetoanaerobium noterae, Clostridium aceticum, Butyribacterium methylotrophicum, Clostridium acetobutylicum, Clostridium thermoaceticum, Eubacterium limosum, Clostridium ljungdahlii (especially strains Clostridium ljungdahlii PETC, Clostridium ljungdahlii ERI2, Clostridium ljungdahlii C-01 and Clostridium ljungdahlii O-52 ), Peptostreptococcus productus and Clostridium carboxydivorans (especially strains
• Particularly preferred bacteria are Clostridium ljungdahlii and Clostridium carboxydivorans .
• the process of this embodiment of the first aspect of the present invention results in separate product streams comprising ethanol.
• Preferably said ethanol product streams are combined and passed to a common ethanol treatment/separations section, avoiding unnecessary duplication of equipment.
• both the solution comprising acetic acid from step (a) and the gaseous mixture comprising carbon monoxide and hydrogen from step (b) are passed to a common (second) fermentation step in step (c).
• the present invention provides a process for the production of ethanol, said process comprising:
• An obvious advantage of this embodiment is that only one further fermentation step is required in the process, rather than two. Further, however, not only can the anaerobic acetogenic bacteria suitable for ethanol production from carbon monoxide and hydrogen tolerate the acetic acid, but this embodiment actually results in a yet further increase in ethanol selectivity per unit of feedstock converted. In particular, it is known that the anaerobic acetogenic bacteria suitable for ethanol production from carbon monoxide and hydrogen, although highly selective for ethanol, generally also produce competing products, such as acetic acid, the production of which it is generally desired to minimise.
• US 2003/0211585 seeks to control the conditions in the fermentation process to favour ethanol production over acetic acid, and in such a process any acetic acid formed is recycled to the fermentation step.
• acetic acid is deliberately introduced into the fermentation process (second fermentation step) with the gaseous mixture comprising carbon monoxide and hydrogen to inhibit acid formation in the second fermentation step, resulting in a net acetic acid conversion, rather than any production, in this step.
• H 2 present in the gaseous mixture from the gasification step (b) can also be utilized to convert the acetic acid from step (a) to ethanol, giving the following equations for the conversion of the fermentable components of the initial feedstock: C 6 H 12 O 6 ⁇ 3CH 3 COOH (4) 3CH 3 COOH + 6H 2 ⁇ 3C 2 H 5 OH + 3 H 2 O (5)
• the presence of hydrogen results in reduced CO 2 and increased ethanol compared to the "conventional" overall fermentation route represented by equation (3) above.
• the second aspect of the present invention results in a further increased ethanol selectivity per unit of feedstock converted.
• the carbon monoxide present in the feedstream to the second fermentation step is a poison to many bacteria, including those present in the first fermentation step.
• a further advantage of this embodiment is that separate pasteurisation or sterilisation of the bacteria in the solution from the first fermentation may be avoided, the carbon monoxide acting to sterilise the solution in-situ in the second fermentation step.
• the second fermentation step including the preferred conditions to favour ethanol production over acetic acid are preferably as described in US 2003/0211585 , useful bacteria including, without limitation, those described in US 2003/0211585 and US 2007/0275447 , namely Acetogenium kivui , Acetobacterium woodii, Acetoanaerobium noterae, Clostridium aceticum, Butyribacterium methylotrophicum, Clostridium acetobutylicum, Clostridium thermoaceticum, Eubacterium limosum, Clostridium ljungdahlii (especially strains Clostridium ljungdahlii PETC, Clostridium ljungdahlii ERI2, Clostridium ljungdahlii C-01 and Clostridium ljungdahlii O-52 ) , Peptostreptococcus productus and Clostridium carboxydivorans (
• Particularly preferred bacteria for step (c) for this embodiment are Clostridium ljungdahlii and Clostrirlium carboxydivorans .
• the ratio of ethanol over acetate can be increased by manipulating the bacteria in the bioreactor, in particular by reducing the redox potential or increasing the NAD(P)H to NAD(P) ratio in the fermentation broth after said bacteria achieves a stable cell concentration in said bioreactor.
• This manipulation can be achieved by altering at least one parameter selected from the group consisting of nutrient medium contents, nutrient feed rate, aqueous feed rate, operating pressure, operating pH, gaseous substrate contents, gas feed rate, fermentation broth agitation rate, product inhibition step, cell density, substrate inhibition and combinations thereof. Practical examples of this are, for example, supplying an excess ofH2 or a slight excess of CO or limiting the amount of calcium pantothenate in solution
• the ethanol is obtained from step (c) as a dilute solution in water (or two or more dilute solutions in water where two or more further fermentation steps are used in step (c), but which are preferably combined prior to ethanol treatment/separations).
• the dilute ethanol product stream is treated to concentrate and separate the ethanol.
• the actual final purity of ethanol desired will depend on the subsequent intended use, but is typically at least 90 wt%, preferably at least 95 wt% and more preferably at least 99 wt%.
• the preferred technique for treatment/purification is to use distillation.
• ethanol in water cannot be purified by simple distillation to higher than about 95 wt%, at atmospheric pressure, due to the formation of an azeotrope with water.
• the ethanol product is purified to about 90-95 wt% by distillation followed by a drying step, for example on molecular sieve, to give a >99 wt% product.
• alcohols in the product stream such as butanol
• the product ethanol stream from step (c) typically comprises ethanol at a concentration of ethanol in solution of 1 to 5 wt%, more typically in the range 2 to 5 wt%.
• Butanol is usually the next most predominant alcohol, and is typically present at a concentration of butanol in solution of up to 1wt%, for example of 0.2 to 1 wt%, more typically in the range 0.2 to 0.75 wt%, such as 0.4 to 0.75 wt%.
• the initial concentration of ethanol is in the range 2 to 5wt%.
• the rectification operating line is "pinched" close to the vapour-liquid equilibrium curve near to the azeotrope composition.
• the concentration of ethanol in the initial stream is below about 2 wt%.
• the pinch remains at the same point at the top of the curve, and the rectification operating line changes minimally. This means that the reflux ratio, and hence the column duty, does not change significantly as the initial feed composition is increased.
• the following example provides a comparison between the conversion of a typical municipal solid waste (MSW) using a process of gasification followed by fermentation "alone" (comparative), versus a route where 50% of the calorific value of the MSW is converted to ethanol via a first fermentation step to produce acetic acid.
• a typical municipal waste can be represented as:
• the gasification yields (by volume): 36% CO, 10% CO 2 , 50% H 2 and 4% N 2 , which translates as 42.5 kT CO, 4.2 kT of H 2 and 18.6 kT of CO 2 per 100 kT of the initial MSW feed (a typical annual processing capacity).
• a typical CO conversion is 80% and a typical H 2 conversion is 40%, which (assuming 100% selectivity to ethanol i.e. no acetic acid) produces from the fermentation of the syngas 15.7 kT of ethanol and 23.3 kT of CO 2 . (35.6 kT of CO 2 is produced from the first reaction above, and 12.3 kT is consumed in the second reaction above.)
• the overall yields of the ethanol and CO 2 are 15.7 kT of ethanol and 41.9 kT of CO 2 per 100 kT of the initial MSW feed.
• the amount of CO 2 produced compared to ethanol produced equates to 2.66 Te of CO 2 per Te of ethanol.
• the 50% by calorific value of the gasifiable material which is digestible is instead digested to form acetic acid, which is then converted to ethanol via solventogenesis.
• the syngas from the gasification and the acetic acid from the digestion are separately converted to ethanol.
• the net productions of ethanol and CO 2 are 23.2 kT and 35.7 kT respectively.
• the amount of CO 2 produced compared to ethanol produced equates to 1.54 Te of CO2 per Te of ethanol.
• Example 1 is repeated except that the reactions of fermentation to ethanol of the syngas from the gasification and the solventogenesis of the acetic acid are combined in a single reactor as in the preferred second embodiment of the present invention.
• the H 2 present in the syngas can be utilized to convert the acetic acid to ethanol giving the following equations for the process: C 6 H 12 O 6 ⁇ 3CH 3 COOH (4) 3CH 3 COOH + 6H 2 ⁇ 3C 2 H 5 OH + 3 H 2 O (5) (Net reaction for this route: C 6 H 12 O 6 + 6H 2 ⁇ 3C 2 H 5 OH + 3 H 2 O)
• reaction (5) utilises the hydrogen present in the syngas for conversion of the acetic acid to ethanol.
• this is assumed to result in a reduction in the syngas fermentation of hydrogen via equation (2) above (2CO 2 + 6H 2 ⁇ C 2 H 5 OH + 3H 2 O) because of a competition for available hydrogen, but even in this scenario will result in a further net increase in ethanol production and a further net reduction in CO 2 production.
• Example 2 Although the absolute amount of ethanol produced is slightly reduced compared to Example 1 (due principally to a cautious assessment of the acetic acid to ethanol conversion via equation (5)), the net CO 2 production is significantly reduced further still. In this Example, the amount of CO 2 produced compared to ethanol produced equates to only 1.23 Te of CO2 per Te of ethanol.
• reaction (2) does not occur.
• reactions (2) and (5) could both occur this would result in yet a further increase in ethanol and reduction in CO 2 produced.

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